Studies employing mammalian small intestine have provided circumstantial evidence for separate sites for C1 absorption and secretion. According to the model proposed, C1 absorption is a function of the villus cells while C1 secretion results from an inhibition of the absorptive mechanism in the villus cells and stimulation of a secretory process in the cells of the crypts of Lieberkuhn. The proposed research project is designed to provide a detailed description of the driving forces responsible for C1 movement across the limiting membranes of villus and crypt cells of isolated rabbit ileal mucosa in vitro. These studies will be conducted using electrophysiologic techniques to determine: (1) the electrical potential profile; (2) relative membrane resistances and permselective properties of the mucosal and basolateral membranes; (3) intracellular activities of K, C1 and Na; and (4) changes in these parameters which result from stimulatio of C1 absorption or secretion. These studies will further define the site(s) and mechanism(s) of C1 absorption and secretion in mammalian small intestine and provide information about the sites and mechanisms of action of agents which stimulate C1 absorption or secretion. Results from this study provide a basis for the rational treatment of disorders of salt and water transport by mammalian intestine.